Determine if object/embed is forbidden? - javascript

You might know HN, but you maybe also do not like the fact of clicking around in many tabs/going back and forward. I thought about making some page on which both webpage and links from HN are. So I made this: http://goodfrontpage.com/direct
But there are 2 Problems:
First: How to determine if a page doesn't allow in it's http-headers to open it in something like this:
<iframe class="webpage" src="{{post.url}}" ></iframe>
or this:
<object class="webpage" data="http://asfasfasfa.com" >
<embed class="webpage" src="http://asfasffvasf.com" > </embed>
Error: Webpage not accessible!
</object>
This is true for pages like github.com, eff.org or youtube.com
Second: Is there any possibility to fetch the sites in a different way allowing me to display all pages?

If you want to embed a webpage within another one then you should use the iframe element:
<iframe src="http://asfasffvasf.com"/>
You can style this like any other block element, and set an explicit width and height.
Some pages ask browsers not to include them within iframes (using the X-Frame-Options header). I don't think there's an easy way to solve this on the client side, but you could create a simple backend or proxy to request the page you want and return the content. This gets round the iframe restriction because you're now including content from your own domain.
This does have a couple of security issues to be aware of:
You've now made a backend which can be used to download any page on the Internet. There's a denial of service vulnerability if someone makes lots of requests to download huge pages.
The pages you're including will no longer be restricted by the same origin policy. Scripts on those pages will be able to interact with everything on the parent page. This may be a problem if you plan on creating login functionality in the future.

Seems like you are looking for iframe property.It specifies an inline frame.
An inline frame is used to embed another document within the current HTML document.
<iframe src="http://asfasfasfa.com"></iframe>

Related

Security concerns with same origin iframes [duplicate]

I am planning to create an open source education web app where people can add and edit the content (a bit like Wikipedia).
However I wish to add another feature that allows the user to add their own interactive content using JavaScript. (similar how JSFiddle does it)
What are the security concerns in doing this?
Optional question: How can these issues be overcome?
Yes you could use HTML5 Sandbox to only load user scripts in an IFrame.
You should only host user content from a different domain than your main site. This will prevent any XSS attack if an attacker convinces a user to visit the page directly (outside of the sandbox). e.g. if your site is www.example.com you could use the following code to display the sandboxed IFrame (note .org rather than .com, which is an entirely different domain):
<iframe src="https://www.example.org/show_user_script.aspx?id=123" sandbox="allow-scripts"></iframe>
This will allow scripts, but forms and navigation outside of the IFrame will be prevented. Note that this approach could still risk a user hosting a phishing form to capture credentials. You should make sure that the boundaries between your site and the user content are clear within the user interface. Even though we haven't specified allow-forms, this only prevents a form from being submitted directly, it does not prevent form elements and JavaScript event handlers from sending any data to an external domain.
The HTML5 Security Cheat Sheet guidance on OWASP states this is the purpose of the sandbox:
Use the sandbox attribute of an iframe for untrusted content
You should test whether sandbox is supported first, before rendering the IFrame:
<iframe src="/blank.htm" sandbox="allow-scripts" id="foo"></iframe>
var sandboxSupported = "sandbox" in document.createElement("iframe");
if (sandboxSupported) {
document.getElementById('foo').setAttribute('src', 'https://www.example.org/show_user_script.aspx?id=123');
}
else
{
// Not safe to display IFrame
}
It is safer to do it this way by dynamically changing the src rather than redirecting away if sandboxSupported is false because then the iframe will not accidentally be rendered if the redirect doesn't happen in time.
As a simpler alternative, without the need to check whether the sandbox is supported, you can use the srcdoc IFrame attribute to generate the sandboxed content, making sure that all content is HTML encoded:
e.g.
<html><head></head><body>This could be unsafe</body></html>
would be rendered as
<iframe srcdoc="<html><head></head><body>This could be unsafe</body></html>" sandbox="allow-scripts"></iframe>
Or you could construct a data blob object, being careful to HTML encode again:
<body data-userdoc="<html><head></head><body>This could be unsafe</body></html>">
<script>
var unsafeDoc = new Blob([document.body.dataset.userdoc], {type: 'text/html'});
var iframe = document.createElement('iframe');
iframe.src = window.URL.createObjectURL(unsafeDoc);
iframe.sandbox = 'allow-scripts';
</script>
Of course you could also set the unsafeDoc variable from a JSON data source. It is not recommended to load an HTML file, as this has the same problem of it having to be from an external domain, as the attacker could just entice the user to load that directly.
Also, please don't be tempted to write user content into a script block directly. As shown above, data attributes is the safe way to do this, as long as correct HTML encoding is carried out on the user data as it is output server-side.
In these cases you can leave src as blank.html as older browsers that do not support srcdoc will simply load that URL.
As #Snowburnt touches upon, there is nothing stopping a user script from redirecting a user to a site where a drive-by download occurs, but this approach, assuming a user is up to date on patches, and there are no zero day vulnerabilities, this is a safe approach because it protects its end users and their data on your site via the same origin policy.
One big issue is cross-site scripting where users add code that tells the browser to open and run code from other sites. Say they add something that creates an iFrame or a hidden iFrame pointing to a site and starts downloading malicious code.
There's no simple way around it (thanks to Bergi in the comments) to make sure no elements are created and no ajax calls are made.
I've been a member of sites that provided this functionality, but for those sites I paid for my own space so any vulnerabilities I add are inconveniencing my own clients, in that case it's a little more okay to let that slip by since it's not a security leak for everyone.
One way around this is to create customizable controls for the users to use to add interactivity. The plus is that you control the javascript being added, the minus is that your user base will have to request and then wait for you to create them.

Using jQuery/javascript with Google Forms

I am trying to use jQuery/javascript with an iframe containing google form.
Here is the code snippet:
<body>
<iframe id="myFormFrame" src="https://docs.google.com/forms/d/smfjkafj809890dfafhfdfd/viewform?embedded=true" width="760" height="1750" frameborder="0" marginheight="0" marginwidth="0">Loading...</iframe>
<button id="mybtn">Click</button>
<script type="text/javascript">
$('#mybtn').click(function(){
var m=document.getElementById("ss-form");
alert(m.innerHTML);
});
</script>
The button on click should give the innerHTML of the form(which on loading inside iFrame has an id of "ss-form"). But its not working. So what could be the reason(cross domain iframe?)?
And what is the way to make jQuery work with google forms?
If it helps, I am trying to put custom ajax validation in place(for example, the email id field must contain emails from a specific list obtained from different database).
EDIT
Well it looks like a cross domain issue. I had this doubt in mind. But after looking at this article, it looks like possible.
document.getElementById searches the current document, not other documents loaded into frames.
If the framed document was on your own site then you could access the frame and then access the document (via contentDocument) first. Then call getElementById on that.
Since it is cross-origin, that will fail. The reasons for this are obvious if you consider what would happen if Mallory's evil website were to stick your bank's online banking site into a frame while you were logged in.
If you had the cooperation of Google (you don't) then you could pass messages between the frames using postmessage.
Well it looks like a cross domain issue. I had this doubt in mind. But after looking at this article, it looks like possible.
They aren't using a form hosted by Google. They've used Google tools to design the form and then copied the HTML to their own site. If Google ever implement CSRF protection, that will break.

Can I use indexeddb across subdomains?

I'm building a Chrome extension and using the db.js wrapper to utilize the indexeddb. The problem is, I've got several subdomains and I'd like to be able to share the information across them.
When I use the Chrome Dev tools to view Resources, all of the individual subdomains have their own copy of the schema I'm creating, and each has it's own data.
The only thing I knew to try was to set the document.domain but that didn't help. I wasn't surprised.
Documentation on indexeddb is very slim it seems. I keep finding the same 2 or 3 blog posts copied word for word in several different blogs and nothing specifies that this is possible or impossible.
You can't access the same database from multiple subdomains, the access scope is limited to html origin.
html_Origin = protocol + "://" + hostname + ":" + port + "/";
As #Xan mentioned, if you can use a common origin owned by the extension itself, rather than by the content pages, that sounds like it would be by far the easiest solution. If for whatever reason you can't do that (or for readers who got here wanting to know about regular page javascript or Greasemonkey-style userscripts, rather than extensions), the answer is:
Yes, though it's a slightly awkward and takes some work:
Since you're using a number of related subdomains, (rather than completely unrelated domains), there's a technique you can use in that situation. It can be applied to IndexedDB, localStorage, SharedWorker, BroadcastChannel, etc, all of which offer shared functionality between same-origin pages, but for some reason don't respect modifications to document.domain.
(1) Pick one "main" subdomain to for the data to belong to. i.e. if your subdomains are https://a.example.com, https://b.example.com, and https://c.example.com, you might choose to have your IndexedDB database stored under the https://a.example.com subdomain.
(2) Use it normally from all the the https://a.example.com pages.
(3) On https://b.example.com and https://c.example.com, use javascript to set document.domain = "example.com";. Then also create a hidden <iframe>, and navigate it to some page on the https://a.example.com domain (It doesn't matter what page, as long as you can insert a very little snippet of javascript on there. If you're creating the site, just make an empty page specifically for this purpose. If you're writing an extension or a userscript and so don't have any control over pages on the example.com server, just pick the most lightweight page you can find and insert your script into it. Some kind of "not found" page would probably be fine).
(4) The script on the hidden iframe page need only (a) set document.domain = "example.com";, and (b) notify the parent window when this is done. After that, the parent window can access the iframe window and all its objects without restriction! So the minimal iframe page is something like:
<!doctype html>
<html>
<head>
<script>
document.domain = "example.com";
window.parent.iframeReady(); // function defined & called on parent window
</script>
</head>
<body></body>
</html>
If writing a userscript, you might not want to add externally-accessible functions such as iframeReady() to your unsafeWindow, so instead a better way to notify the main window userscript might be to use a custom event:
window.parent.dispatchEvent(new CustomEvent("iframeReady"));
Which you'd detect by adding a listener for the custom "iframeReady" event to your main page's window.
(5) Once the hidden iframe has informed its parent window that it's ready, script in the parent window can just use iframe.contentWindow.indexedDB, iframe.contentWindow.localStorage, iframe.contentWindow.BroadcastChannel, iframe.contentWindow.SharedWorker instead of window.indexedDB, window.localStorage etc. ...and all these objects will be scoped to the https://a.example.com origin - so they'll have the this same shared origin for all of your pages!
The "awkward" part of this technique is mostly that you have to wait for the iframe to load before proceeding. So you can't just blithely initialize IndexedDB in your DOMContentLoaded handler, for example. Also you might want to add some error handling to detect if the hidden iframe fails to load correctly.
Obviously, you should also make sure the hidden iframe is not removed or navigated during the lifetime of your page... OTOH I don't know what the result of that would be, but very likely bad things would happen.
And, a caveat: setting/changing document.domain can be blocked using the Feature-Policy header, in which case this technique will not be usable as described.
However, there is a significantly more-complicated generalization of this technique, that can't be blocked by Feature-Policy, and that also allows entirely unrelated domains to share data, communications, and shared workers (i.e. not just subdomains off a common superdomain). #Xan alludes to it in point (2) of his answer:
The general idea is that, just as above, you create a hidden iframe to provide the correct origin for access; but instead of then just grabbing the iframe window's properties directly, you use script inside the iframe to do all of the work, and you communicate between the iframe and your main window only using postMessage() and addEventListener("message",...).
This works because postMessage() can be used even between different-origin windows. But it's also significantly more complicated because you have to pass everything through some kind of messaging infrastructure that you create between the iframe and the main window, rather than (for example) just using the IndexedDB API directly in your main window's code.
HTML-based storage (indexedDB, localStorage) in Chrome extensions behaves in a way that might not be expected, but it's perfectly natural.
In the background page, the domain is chrome-extension://yourextensionid/, and this is shared by all extension pages and is persistent.
In the content scripts though, you're sharing the HTML storage with the domain you're operating on. This makes life difficult if you want it to share/persist things. Note that sometimes this behavior is actually helpful.
The universal solution is to keep the DB in a background script, and communicate data/requests by means of Messaging API.
This was the usual solution for localStorage use until chrome.storage came along. But since you're using a database, you don't have a ready extension-friendly replacement.

Need to change #src of a parent iframe from within child iframe

I have the following HTML markup (don't ask....)
- document //main site
- <iframe> //my site
- <iframe> //site within my site
- <frame>
- <a onclick="JavaScript:parent.parent.location.href='http://bla.com;return false;'">
Basically, main site is calling my site in an iframe. I, in turn, also have an iframe on my site where I'm calling 3rd site. The third site has a frameset with a frame in it that has a link. When clicking on this link, it has to change the url of my site. My site and my child site are on the same domain. When I'm running my site as "stand-alone" (not in iframe) the above code works fine in all browsers.
Once I open my site in an iframe of the main site, it looks like the above code is trying to change the source of the main site. In FireFox I get a console message "Access to property denied". In IE it opens up a new window with my site not in the main site anymore.
What is the correct JavaScript to change the #src attribute on my site when I'm within an iframe?
You are banging your head against the wall that is the same origin policy here. This is XSS country and strictly forbidden, no way around it, unless both domains agree to talk together.
You can read more about cross domain communication using iframes, but again, unless the different domain agree to talk together, you are out of luck.
Although this might seem frustrating, be glad of this rule next time you use homebanking ;)
Can you try something like this
<document> //main site
<iframe id="my_iframe"> //your site
<iframe> //site within your site
<frame>
<a onclick="JavaScript:Top.document.getElementById('my_iframe').location.href='http://bla.com;return false;'">
Top refers to the main window, and then getElementById('my_iframe') will give you your iframe element.
I believe that you're trying to do communication between different pages.
You may take a look this API: HTML5 Cross Document Messaging
Basically, if you want to tell the parent iframe to navigate to a certain url, you can do this:
In the site within my site html:
// onclick of your anchor, post message (an event) with an expected origin
window.postMessage("http://bla.com", "www.sitewithinmysite.com");
In my site html:
// listen to the event "message"
window.addEventListener("message", messageHandler, true);
function messageHandler(e) {
// only recognize message from this origin
if (e.origin === "www.sitewithinmysite.com") {
// then you can navigate your page with the link passed in
window.location = e.data;
}
}
You might want to have the pages communicate using AJAX. Have the site that needs to change its URL listen by long polling to to a node.js server.

Is it possible to use jQuery to grab the HTML of another web page into a div?

I am trying to integrate with the FireShot API to given a URL, grab HTML of another web page into a div then take a screenshot of it.
Some things I will need to do after getting the HTML
grab <link> & <script> from <head>
grab <body> into <div>
But 1st, it seems when I try to do a
$.get("http://google.com", function(data) { ... });
I get a 200 in firebug colored red. I think it has to do with sites not allowing you to grab their page with JS? Then is opening a window the best I can do? But how might I control the other page with jQuery or call fsapi on that page?
UPDATE
I tried to do something like below to do something when the new window is ready, but FireBug says "Permission denied to access property 'document'"
w = window.open($url.val());
setTimeout(function() { // if I dont do this, I always get about:blank, is there a better way around this?
$(w.document).ready(function() {
console.log(w.document.body);
});
}, 1000);
I believe the cross-site security setup within Javascript is basically blocking this. You'd likely have to proxy the content through your own domain.
There are a couple other options I think for break the cross-site security constraints, but I'm not sure I'd promote them.
If the "another page" locates within the same domain of your hosting page, yes, you can. Please refer to jQuery's $().load() API.
Otherwise, you're disallowed to do so by the browser's Cross-Site Security Policy. At this moment, you can choose to use iFrame instead of DIV.
Some jQuery plugins, e.g. thickbox provides ability to load pages to appropriate container automatically.
Unless I am correct, I do not believe you can AJAX a page cross domain (e.g. from domain1.com to domain2.com). To get around this, you can have a PHP "proxy" script that does the "getting" of the page and then pass it to JS.
For example, in JS you would get() http://mydomain.com/get/?domain=http://google.com and then do what you need to do!

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